A 23-year-old man has pleaded guilty to a charge of unlawful assembly, following a brawl in the grounds of Hutt Valley High School yesterday.
Police said a series of fights broke out shortly before 3pm after a group of three adults and six youths arrived at the school and confronted a student about a previous fight.
The school field erupted into a brawl when about 30 students went to aid their schoolmate.
About a dozen police were needed to quell the fighting and arrest the nine members of the group, who the school's principal said were wearing gang colours.
All nine were charged with unlawful assembly.
One, Cody Samuels, 23, pleaded guilty in Lower Hutt District Court to the charge, Radio New Zealand reported. He was remanded on bail to be sentenced next month.
The eight others, aged between 14 and 20, all appeared in the Youth Court and were remanded on bail to reappear in the court next week.
The school today said it had arranged with the Education Ministry to have security guards patrol the school in light of the incident.
The only reported injury from the melee was that to a female student hit on the head by a flying rock.
None of those arrested were involved with the school.